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Human Anatomy

Picture of the Intestines

The intestines are a long, continuous tube running from the stomach to the anus. Most absorption of nutrients and water happen in the intestines. The intestines include the small intestine, large intestine, and rectum.

The small intestine (small bowel) is about 20 feet long and about an inch in diameter. Its job is to absorb most of the nutrients from what we eat and drink. Velvety tissue lines the small intestine, which is divided into the duodenum, jejunum, and ileum.

The large intestine (colon or large bowel) is about 5 feet long and about 3 inches in diameter. The colon absorbs water from wastes, creating stool. As stool enters the rectum, nerves there create the urge to defecate.

Intestine Conditions

Stomach flu (enteritis): Inflammation of the small intestine. Infections (from viruses, bacteria, or parasites) are the common cause.

Small intestine cancer: Rarely, cancer may affect the small intestine. There are multiple types of small intestine cancer, causing about 1,100 deaths each year.

Celiac disease: An "allergy" to gluten (a protein in most breads) causes the small intestine not to absorb nutrients properly. Abdominal pain and weight loss are usual symptoms.

Carcinoid tumor: A benign or malignant growth in the small intestine. Diarrhea and skin flushing are the most common symptoms.

Intestinal obstruction: A section of either the small or large bowel can become blocked or twisted or just stop working. Belly distension, pain, constipation, and vomiting are symptoms.

Colitis: Inflammation of the colon. Inflammatory bowel disease or infections are the most common causes.

Diverticulosis: Small weak areas in the colon's muscular wall allow the colon's lining to protrude through, forming tiny pouches called diverticuli. Diverticuli usually cause no problems, but can bleed or become inflamed.

Diverticulitis: When diverticuli become inflamed or infected, diverticulitis results. Abdominal pain and constipation are common symptoms.

Irritable bowel syndrome (IBS): Irritable bowel syndrome, also known as IBS, is an intestinal disorder that causes irritable abdominal pain or discomfort, cramping or bloating, and diarrhea or constipation.

Rectal prolapse: Part or all of the wall of the rectum can move out of position, sometimes coming out of the anus, when straining during a bowel movement.

Intussusception: Occurring mostly in children, the small intestine can collapse into itself like a telescope. It can become life-threatening if not treated.